The disclosure of Japanese Patent Application No. 11-256164 filed on Sep. 9, 1999 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a fuel supplying apparatus and method for an internal combustion engine.
2. Description of the Related Art
In internal combustion engines, automotive engines and the like, an engine that directly injects fuel into a combustion chamber for the purpose of improving fuel economy and the like has recently been commercialized. As such, a high pressure of fuel supplied to the fuel injection valve is required in order to inject fuel from the fuel injection valve into the combustion chamber and thus overcome the high pressure in the combustion chamber. Therefore, fuel fed from a fuel tank by a feed pump is pressurized by a high-pressure fuel pump and delivered to the fuel injection valve. A known fuel supplying apparatus having a high-pressure fuel pump as mentioned above is described in Japanese Patent Application Laid-Open Nos. 10-76618 and 10-176619. A fuel supplying apparatus described in these laid-open patent applications is shown in FIG. 9.
As shown in FIG. 9, a high-pressure fuel pump 101 of the fuel supplying apparatus has a plunger 103 that is reciprocated within a cylinder 102 by rotation of a cam 100, and a pressurizing chamber 104 defined by the cylinder 102 and the plunger 103. Connected to the pressurizing chamber 104 are a suction passage 107 communicating with a feed pump 106 for feeding fuel from a fuel tank 105, a spill passage 108 that lets fuel out of the pressurizing chamber 104 to return fuel to the fuel tank 105, and a delivery passage 110 for delivering pressurized fuel from the pressurizing chamber 104 toward a fuel injection valve 109. The high-pressure fuel pump 101 has a spill valve 111 that opens and closes the communication of the spill passage 108 and the suction passage 107 with the pressurizing chamber 104.
When the plunger 103 is moved in such a direction as to increase the capacity of the pressurizing chamber 104 (downward in the drawing) while the spill valve 111 is in an open state, that is, when the high-pressure fuel pump 101 is in the suction stroke, fuel is drawn from the suction passage 107 into the pressurizing chamber 104. When the spill valve 111 is closed during a movement of the plunger 103 in the pressurizing chamber 104-capacity reducing direction (upward in the drawing), that is, during the fuel ejection stroke of the high-pressure fuel pump 101, the communication of the suction passage 107 and the spill passage 108 with the pressurizing chamber 104 is closed, so that fuel is delivered from the pressurizing chamber 104 toward the fuel injection valve 109 via the delivery passage 110.
In this high-pressure fuel pump 101, fuel is delivered toward the fuel injection valve 109 only during the closed valve period of the spill valve 111 during the ejection stroke of the pump, the amount of fuel delivered is adjusted by adjusting the closed period of the spill valve 111 through control of the valve closure start timing of the spill valve 111. That is, the amount of fuel delivered is increased by increasing the closed valve period of the spill valve 111, and is reduced by reducing the closed valve period. When the amount of fuel delivered is adjusted, the pressure of fuel delivered to the fuel injection valve 109 (fuel pressure) is controlled to a target value that is determined in accordance with the operation state of the engine, so that the amount of fuel injected from the fuel injection valve 109, which is determined by the fuel pressure and the fuel injection duration, becomes equal to a proper amount.
Thus, since fuel fed from the feed pump 106 is pressurized by the high-pressure fuel pump 101 and the pressurized fuel is delivered toward the fuel injection valve 109, the engine is able to precisely perform fuel injection.
The amount of fuel delivered from the high-pressure fuel pump 101 is affected by the cam speed (i.e., the amount of movement of the plunger 103 per unit angle rotation of the cam 100) that occurs when the closure of the spill valve 111 starts. The cam speed at the start of closure of the spill valve 111 does not necessarily change at a constant changing rate (with a constant gradient) with respect to changes of the start timing of closure of the spill valve 111. More specifically, the changing rate (gradient) of the cam speed at the start of closure of the spill valve 111 with respect to changes in the start timing of closure of the spill valve 111 greatly fluctuates based on the phase of the cam. If the amount of fuel delivered is adjusted by changing the start timing of closure of the spill valve 111 so as to control the fuel pressure to a target value, the change of the valve closure start timing does not readily adjust the amount of fuel delivered (fuel delivery amount) in an adequate fashion, thus resulting in considerable fluctuations in the fuel pressure during the control of the fuel pressure to the target value.
Accordingly, it is one object of the invention to provide a fuel supplying apparatus for an internal combustion engine that improves the controllability of the amount of fuel delivered, by appropriately adjusting the amount of fuel delivered in accordance with changes of the closure start timing of a spill valve.
A first aspect of the invention provides a fuel supplying apparatus for an internal combustion engine, having a fuel pump that draws fuel into a pressurizing chamber and delivers fuel toward a fuel injection valve of the internal combustion engine by changing a capacity of the pressurizing chamber based on a relative movement between a cylinder and a plunger caused by a rotation of a cam. The apparatus also includes a spill valve that opens and closes a communication between the pressurizing chamber and a spill passage for letting fuel out of the pressurizing chamber, wherein an amount of fuel delivered from the fuel pump toward the fuel injection valve is adjusted by controlling a closed valve period of the spill valve. The fuel supplying apparatus includes a controller that controls the closed valve period of the spill valve by changing a valve closure start timing of the spill valve so that an amount of fuel that needs to be delivered from the fuel pump for fuel injection from the fuel injection valve is provided. The apparatus is configured so that the valve closure start timing of the spill valve that provides a maximum amount of fuel that needs to be delivered occurs within a predetermined cam angle range in which an amount of the relative movement between the cylinder and the plunger occurring during rotation of the cam changes with a constant gradient with respect to a change in a phase of the cam.
Since the valve closure start timing of the spill valve that provides the maximum amount of fuel that needs to be delivered is located within the predetermined cam angle range in which the amount of the relative movement between the cylinder and the plunger occurring during rotation of the cam changes with a constant gradient with respect to a change in the phase of the cam, the cam speed at the start of closure of the spill valve changes at a substantially constant rate even when the valve closure start timing of the spill valve is changed (i.e., delayed) in order to adjust the amount of fuel delivered from the fuel pump. The cam speed at the start of closure of the spill valve affects the amount of fuel delivered from the fuel pump. However, if the cam speed at the start of closure of the spill valve changes with a constant rate as mentioned above, it is possible to properly adjust the fuel delivery amount by changing the closure start timing of the spill valve, so that the controllability of the fuel delivery amount can be improved.
In the above-described aspect, the controller may end a closure of the spill valve when a position of the cam is near a top dead center, and the valve closure start timing of the spill valve that provides the maximum amount of fuel that needs to be delivered may be set so that the valve closure start timing exists near a most advanced point within the predetermined cam angle range.
Therefore, the changing of the closure start timing of the spill valve for the purpose of adjusting the fuel delivery amount can be performed in a broad range from the vicinity of the most advanced point to a point at which the cam reaches the top dead center, all within the predetermined cam angle range (i.e., the range in which the change in cam speed with respect to changes in the phase of the cam is constant).
In one embodiment, a cam profile may be set such that the valve closure start timing of the spill valve that provides the maximum amount of fuel that needs to be delivered exists within the predetermined cam angle range. Therefore, since the cam profile of the cam of the fuel pump is set such that the valve closure start timing of the spill valve that provides the maximum amount of fuel that needs to be delivered exists within the predetermined cam angle range, the cam speed at the start of closure of the spill valve changes with a constant amount of change with respect to a change of the closure start timing of the spill valve that is made in order to adjust the amount of fuel delivered from the fuel pump. Hence, it becomes possible to properly adjust the fuel delivery amount by changing the closure start timing of the spill valve, so that the controllability of the fuel delivery amount can be improved.
In another embodiment, a number of times that fuel is delivered during a predetermined amount of rotation of the cam may be set such that the valve closure start timing of the spill valve that provides the maximum amount of fuel that needs to be delivered exists within the predetermined cam angle range. Therefore, since the number of times of delivering fuel during the predetermined angle of rotation of the cam is set such that the valve closure start timing of the spill valve that provides the maximum amount of fuel that needs to be delivered exists within the predetermined cam angle range, the cam speed at the start of closure of the spill valve changes with a constant amount of change with respect to a change of the closure start timing of the spill valve that is made in order to adjust the amount of fuel delivered from the fuel pump. Hence, it becomes possible to properly adjust the fuel delivery amount by changing the closure start timing of the spill valve, so that the controllability of the fuel delivery amount can be improved.
In another embodiment, an inside diameter of the pressurizing chamber may be set such that the valve closure start timing of the spill valve that provides the maximum amount of fuel that needs to be delivered exists within the predetermined cam angle range. Therefore, since the inside diameter of the pressurizing chamber is set such that the valve closure start timing of the spill valve that provides the maximum amount of fuel that needs to be delivered exists within the predetermined cam angle range, the cam speed at the start of closure of the spill valve changes with a constant amount of change with respect to a change of the closure start timing of the spill valve that is made in order to adjust the amount of fuel delivered from the fuel pump. Hence, it becomes possible to properly adjust the fuel delivery amount by changing the closure start timing of the spill valve, so that the controllability of the fuel delivery amount can be improved.